Many electronic circuits require pulsed supplies of power and various devices are known that take input power from a power source and provide appropriately pulsed output power. One example of such a device is a switched mode power supply, which utilizes one or more switching elements to generate the pulses that are output at the required frequency. The frequency is dependent on the design of the power supply and can be from approximately 100 kHz to 2 MHz. A duty cycle of the output pulses is dependent on the load of the power supply and the input voltage, and the amplitude of the current pulses can be several times the average input current.
It will be apparent that whenever a switching element is used to switch power appearing from an input power source, electromagnetic interference is generated that can be conducted back to the power source and cause interference. This can be particularly disadvantageous at radio frequencies, which can cause interference with radio communication systems.
Accordingly, it is known to use Electromagnetic Compatibility (EMC) filters between the power source and the switching elements, for example of the switched mode power supply devices, to filter out the emissions. The EMC filters are passive, with the filtering being carried out by various combinations of capacitors and inductors. The component values are selected so that the emissions are attenuated to meet the conducted emission requirements. Furthermore, the inductors have to operate with the peak currents without saturating. Therefore, as currents get higher and the frequencies get lower, the capacitor and inductor values must increase resulting in components that are physically larger, causing an increase in space requirements and costs.